This invention relates generally to the field of photometric, fluorometric and nephelometric analysis and, more specifically, to a cuvet, and associated apparatus and methods employed in the use of same in association with spectrophotometers, fluorometers, nephelometers and the like.
Current photometric analysis techniques for chemical analysis of blood serum or the like employ spectrophotometers. As described in greater detail in U.S. Pat. No. 3,998,594 of Horne, entitled "Cuvette For Automatic Chemical Testing Apparatus" and issued on an application filed Nov. 26, 1975, common types of spectrophotometers and the like employ removable cells, or cuvets, to contain the sample while the transmittance or other light measurements are being made by the spectrophotometer. Typically, a specimen from a test tube or other reservoir is first deposited into the open top of the cuvet by pouring or by use of a hand-held pipetting device, or pipette, such as shown in U.S. Pat. No. 3,815,790 of Allen and Lee, entitled "Precision Liquid Pipetting Devices" and issued from an application filed Sept. 18, 1972. If not added before, reagent is then often added to the cuvet. It is sometimes necessary to stir or heat, or both stir and heat the resulting mixture of specimen and reagent, or sample, in the cuvet.
The cuvet is then manually placed in a cuvet holder of the spectrophotometer whereat the cuvet and its sample at a transparent window portion, or windows, of the cuvet are interposed between a photoelectric transducer and, except for fluorometric measurements, a source of light of selected wave length, or other radiant source. The transducer produces an electrical signal that has a particular relationship with respect to the amount of light which has been absorbed or transmitted by the sample in the cuvet. The added reagent and light absorbence characteristics for certain types of chemical tests are known and the electrical signal from the transducer is converted to an indication of the constituents present in the sample based upon that knowledge. This information is displayed on meters of the spectrophotometer.
Known cuvets vary in their configuration and material depending on such factors as the degree of accuracy desired, the wavelength of light being used for the spectroanalysis and the mechanical design of the cuvet holder of the particular spectrophotometer being utilized. Traditionally, cuvets have been made of pyrex for use in the visible range of the light spectrum where glass transmits light and have been made of quartz for use in the ultraviolet region. Because of cost, such cuvets are generally used repetitively. In recent years, use of disposable cuvets made of plastic has increased for application in the visible region of the spectrum and in situations where light characteristics of plastic are adequate for the degree of accuracy desired. Reference may be had to the aforementioned U.S. Pat. Nos. 3,998,594 and 3,627,432 of Bergmann, entitled "Reaction Vessel For Use In Photometric Measurements" and issued from an application filed Apr. 29, 1969.
Generally, all cuvets for use with spectrophotometers comprise elongate, open-ended containers with aligned, transparent sections of opposed sidewalls, on their lower portions, which transparent sections are referred to herein as "windows". The windows are often planer wall sections which are visually distinguishable by configuration from the remaining parts of the cuvet, but such is not necessarily the case if great accuracy is not a critical factor. Generally, the entire cuvet is transparent, but functionally, transparency is only required for the windows. The sample is contained in the cuvet between the windows, and the windows are located at a level such that they align with the light source and photoelectric transducer when inserted in the cuvet holder. The distance between the windows, i.e., the thickness of the liquid sample, is generally standardized as 10 millimeters.
For each sample the steps of filling or loading the cuvet, inserting the cuvet in the cuvet holder, stirring and/or heating the sample in the cuvet and then removing and reloading the cuvet are repeated. Thus, each test requires the operator to load the cuvet by pouring in the sample or specimen and reagent from a test tube or the like into its open top or by using a transfer pipette device, such as the type shown in the aforementioned U.S. Pat. No. 3,815,790.
This procedure presents problems or disadvantages. First, because of the relatively small size of the cuvet opening, being on the order of only one centimeter in diameter, pouring liquids into a series of cuvets is tedious and time consuming and presents problems of spillage and resultant contamination due to necessary manual handling. The use of transfer pipettes also presents contamination problems unless a clean pipette is used for each test, since each new sample may contain either a different specimen or a different reagent. The manual handling of the cuvet required by both loading procedures can also cause smudges on the windows which impairs accuracy.
In more recent years, so called "flow through" spectrophotometers have been developed which have a stationary cell that is filled with specimen and reagents while mounted within the spectrophotometer by means of tubal connections. An example of such a device is shown in U.S. Pat. No. 3,869,215 of Nolan, entitled "Sample Cell Assembly Having A Heat Conductive Chamber Surrounded An Electrothermal Heating Layer". In that device the reagent and specimen are entered into the top of the cell through tubal connections, and the sample is drained out of the bottom of the cell upon completion of the test. Other flow-through spectrophotometers are known in which liquid samples are drawn up into the cell by means of pressure. Generally, these devices also have contamination problems because the same cell is repeatedly used for different samples. In addition, measurement problems are caused by development of air bubbles in the sample and the inability to inspect the cell for such air bubbles or contaminants before performance of the measurement. Further, in most flow through spectrophotometers, no means is provided for saving the sample upon completion of the test.